Many times we see text message manipulation via the Internet, or using a GSM module. But in this case an inexpensive cellphone is used as the communication interface. The vibration motor has been removed and those connections are monitored to signal incoming messages. Wire leads were soldered to the keypad contacts which allow an Arduino to send out text messages when there is a problem with watering. This isn’t an iron-clad system, as any incoming message will trigger the system and outgoing messages are limited to saved drafts. But a bit of creative programming and we’re sure more functionality could be squeezed out of this hardware.

With a project that I’ll be doing i will use a phone but connect to the serial and use at codes like the gsm module. It seems much easier if you can find a phone that has a serial connection. But nonetheless, it’s a cool project.

There was a linking awhile back about using a $25 GPRS/GSM modem with an arduino. http://hackaday.com/2010/10/18/cheap-and-easy-sms-via-gsm-for-your-mcu/
The modem works on the AT&T network, I just need to get a go-phone to use it on its own (I used my SIM card from my phone). A note, though: If you do use a go-phone SIM, activate the SIM ONLY with the end device you plan on using. Usually the SIMs become device locked for a certain time period following activation.

With that in mind, one can ditch the ringer motor method and make things a little more creatively. For instance, you could send a text with the message “Set water @ 5:00PM”, and you could update an automated timer setup. Pretty neat stuff.

This is a very poor design. An old Nokia will expose a simple serial interface for sending and receiving SMS. It is trivial to read and parse SMS and act on only valid messages. (I know this because I’ve done it).

I see this more as a proof of concept, with certain (already mentioned) security features to add as needed. Still I think the other way around is better: automate the watering (with capacitive sensors, or timers when drip-irrigating) and send out a SMS, if something goes wrong.

SMS systems always make me wonder if it is really worth it. You have to pay to get a phone on the GSM network (in my area, at least $10 per month) and that seems like a lot to be able to water a plant from anywhere you get cellphone reception.